Titanosilicate is a type of zeolite having the same crystalline structure as ZSM-5 and having the composition xTiO2.(1-x)SiO2. Therein, Si in the crystal lattice is replaced with Ti instead of Al, and a preparation method thereof is disclosed by U.S. Pat. No. 4,410,501 to Tarammasso.
Titanosilicate is found to have activity in oxidation reactions of several kinds of organic compounds using hydrogen peroxide as an oxidant. For example, titanosilicate is known for use as a catalyst in a hydroxylation reaction of an aromatic compound, an epoxidation reaction of an olefin, for production of an alcohol or a ketone by oxidation of an alkane and for production of a ketone oxime by ammoximation of a ketone.
A smaller primary particle is generally advantageous for obtaining a catalyst having high activity, and a diameter of a micro crystalline particle of submicron order which is formed at first in a production process (hereinafter referred to as a primary particle) is preferable. However, from a practical view point, a smaller primary particle is difficult to handle, e.g., in isolation and separation of the catalyst. As a result, the advantage for use as a solid catalyst is lost.
On the other hand, titanosilicate is prepared using expensive reagents. As a result, a small loss in handling disadvantageously increases the cost of production, such that recovery to a high extent is necessary. In order to achieve economy of production, formation of a large particle which is formed by a combination of primary particles, (hereinafter referred to as a secondary particle) having the properties of a primary particle and also having a good handling property as a catalyst is needed to allow for practical use.
However, in the secondary particle prepared according to the known method, mechanical strength of the secondary particle is very small. This is because the primary particle of titanosilicate fine crystal prepared by hydrothermal synthesis is simply contacted at the boundary of the primary particle, and is not firmly connected mutually via a chemical bond. That is, when such a titanosilicate catalyst is used, it is easily decomposed to primary particles and the handling property, such as a filtration process, is not satisfactory.
A preparation method for a catalyst having excellent mechanical strength and handling properties is disclosed by U.S. Pat. No. 4,701,428. According to this method, by combining primary particles of titanosilicate with one another using a silica oligomer as a binder in a molar ratio of silica oligomer to titanosilicate of from 0.05 to 0.11, a catalyst having increased mechanical strength and an increased secondary particle diameter is obtained.
However, in this method, titanosilicate powder obtained by hydrothermal synthesis is necessarily dispersed in tetrapropylammonium hydroxide solution and silica oligomer, each prepared individually. The slurry is then rapidly dried using an apparatus such as a spray drier. This method is disadvantageous in that many steps, expensive raw materials and complex procedures and apparatus are needed. Furthermore, in this method, the combination part of the primary particles is an amorphous substance having a structure different from the primary particle of a crystalline substance. That is, the mechanical strength thereof is less than that of the crystalline part. Other disadvantages are a loss of catalyst due to dissolution under alkaline conditions and a decrease of catalytic active points per unit weight of a catalyst.
In view of the above, an object of the present invention is to provide a titanosilicate particle having excellent handling properties and catalytic activity. Yet another object of the present invention is to provide a method of preparing a dihydric phenol by selective hydroxylation of a monohydric phenol, an epoxy compound by selective epoxidation of an olefin, or a method of preparing a ketoxime compound by a selective ammoximation reaction.